Algorithms Exercise 1

Imports



In [1]:

    
%matplotlib inline
from matplotlib import pyplot as plt
import numpy as np

Word counting

Write a function tokenize that takes a string of English text returns a list of words. It should also remove stop words, which are common short words that are often removed before natural language processing. Your function should have the following logic:

Split the string into lines using splitlines.
Split each line into a list of words and merge the lists for each line.
Use Python's builtin filter function to remove all punctuation.
If stop_words is a list, remove all occurences of the words in the list.
If stop_words is a space delimeted string of words, split them and remove them.
Remove any remaining empty words.
Make all words lowercase.



In [2]:

    
def tokenize(s, stop_words= None, punctuation='`~!@#$%^&*()_-+={[}]|\:;"<,>.?/}\t'):
    """Split a string into a list of words, removing punctuation and stop words."""
    # YOUR CODE HERE
    #list comprehension
    w = []
    for line in s.splitlines():
        w.extend(line.split(' '))
    w = [''.join(filter(lambda c: c not in punctuation, s)) for s in w]
    if isinstance(stop_words, str):
        stop_words = stop_words.split(' ')
    if stop_words is not None:
        w = [s for s in w if s not in stop_words]
    w = [s.lower() for s in w if s]
    return w



In [3]:

    
assert tokenize("This, is the way; that things will end", stop_words=['the', 'is']) == \
    ['this', 'way', 'that', 'things', 'will', 'end']
wasteland = """
APRIL is the cruellest month, breeding
Lilacs out of the dead land, mixing
Memory and desire, stirring
Dull roots with spring rain.
"""

assert tokenize(wasteland, stop_words='is the of and') == \
    ['april','cruellest','month','breeding','lilacs','out','dead','land',
     'mixing','memory','desire','stirring','dull','roots','with','spring',
     'rain']

Write a function count_words that takes a list of words and returns a dictionary where the keys in the dictionary are the unique words in the list and the values are the word counts.



In [4]:

    
def count_words(data):
    """Return a word count dictionary from the list of words in data."""
    # YOUR CODE HERE
#     raise NotImplementedError()
    c = {}
    for i in data:
        if i in c:
            c[i] = c[i]+1
        else:
            c[i] = 1
    return c



In [5]:

    
assert count_words(tokenize('this and the this from and a a a')) == \
    {'a': 3, 'and': 2, 'from': 1, 'the': 1, 'this': 2}

Write a function sort_word_counts that return a list of sorted word counts:

Each element of the list should be a (word, count) tuple.
The list should be sorted by the word counts, with the higest counts coming first.
To perform this sort, look at using the sorted function with a custom key and reverse argument.



In [6]:

    
def sort_word_counts(wc):
    """Return a list of 2-tuples of (word, count), sorted by count descending."""
    return list(sorted(wc.items(), key=lambda x: x[1], reverse=True))



In [7]:

    
assert sort_word_counts(count_words(tokenize('this and a the this this and a a a'))) == \
    [('a', 4), ('this', 3), ('and', 2), ('the', 1)]

Perform a word count analysis on Chapter 1 of Moby Dick, whose text can be found in the file mobydick_chapter1.txt:

Read the file into a string.
Tokenize with stop words of 'the of and a to in is it that as'.
Perform a word count, the sort and save the result in a variable named swc.



In [8]:

    
# YOUR CODE HERE
# raise NotImplementedError()
with open('mobydick_chapter1.txt') as txt:
    raw = txt.read()

ts = tokenize(raw, stop_words='the of and a to in is it that as')
count = count_words(ts)
swc = sort_word_counts(count)



In [9]:

    
assert swc[0]==('i',43)
assert len(swc)==848

Create a "Cleveland Style" dotplot of the counts of the top 50 words using Matplotlib. If you don't know what a dotplot is, you will have to do some research...



In [11]:

    
# YOUR CODE HERE
# raise NotImplementedError()
x = np.linspace(1,50,50)
plt.dot









    



---------------------------------------------------------------------------
AttributeError                            Traceback (most recent call last)
<ipython-input-11-c97696146c6d> in <module>()
      2 # raise NotImplementedError()
      3 x = np.linspace(1,50,50)
----> 4 plt.dot

AttributeError: 'module' object has no attribute 'dot'



In [18]:

    
assert True # use this for grading the dotplot



In [ ]: